DE 198 24 761 A1, for example, discloses such a method and such a drive circuit.
FIG. 1 shows the basic design of such a known drive circuit. The series circuit of an inductive load 10 and a switch 20 is arranged between supply terminals 1, 2. The inductive load 10 may, for example, be a solenoid valve of an injection pump in diesel motor vehicles. Also in series with the inductive load 10 are a non-reactive resistor 12 and a further resistor 14 which is used as a current measuring resistor in order to detect the current flowing through the inductive load 10. The anode connection of a diode 16 (whose cathode connection is connected to the supply terminal 2) may be connected between the junction point of the switch 20 and the measuring resistor 14. By way of example, the positive pole of a voltage supply is connected to the supply terminal 2 and reference-ground potential of the voltage supply is connected to the supply terminal 1.
So that the current I flowing through the inductive load 10 can follow a prescribed nominal current Iref as accurately as possible, the known circuit arrangement of FIG. 1 has a pulse width modulator device 30 which turns the switch 20 on and off in a pulse-width-modulated manner. On the input side, the pulse width modulator device 30 has a PI controller 32 which has a pulse width modulator 34 connected downstream of it. A current error signal Ierr which is formed from the difference between the nominal current Iref and the actual current Iact measured across the measuring resistor 14 is supplied to the input of the PI controller 32. Since, in the circuit arrangement shown in FIG. 1, the nominal current Iref is in the form of a digital value, for example in the form of an 18-bit value, it is likewise necessary to convert the analog value (ascertained using the measuring resistor 14) of the actual current Iact into a digital value. An amplifier 22 which is connected, on the output side, to an analog/digital converter 24 and is connected to the measuring resistor 14 is used for this purpose. The digital value for the actual current Iact is available at the output of the analog/digital converter 24.
The problem with such drive circuits is the fact that they are optimized only for a single load situation. This means that an optimum transient response is ensured only in the case of a particular load situation. The actual current through the inductive load follows the prescribed nominal current only in this particular load situation. If, however, the load conditions change, the transient time may vary considerably. In particular, overshooting may result during control, which considerably extends the adjustment time in a disadvantageous manner. This relatively long overshooting is observed, in particular, in the case of large current jumps of the nominal current.